1. Field of the Invention
The invention relates to a device for testing the quality of rope-like materials in the form of yarns, rollings, fiber bands and the like by means of a measuring device which has a microwave generator, a microwave resonator and devices for determining the displacement of the resonant frequency and the widening of the resonance curve due to the rope-like material, and with mechanical devices for transporting the rope-like materials through the measuring volume of the microwave resonator.
2. Description of the Related Art
To test the quality of yarns, rollings and fiber bands, it is necessary to detect quality fluctuations, in particular mass fluctuations, i.e. to check their homogeneity. It is then necessary to detect errors with respect to a mass change. The frequency and intensity of the errors can be used for assessing the quality of the material under test. This quality assessment should be preferably but not exclusively done by means of a laboratory test station. The measurement should be independent of parameters such as moisture, color, grading of the material (e.g. area of cultivation of cotton).
Various devices for testing the quality of rope-like materials are known which, however, have disadvantages. The thickness of, in particular, fiber bands, can be mechanically measured by passing the fiber band through a pair of rollers, at least one of which is movable (DE 298 23 928 U1). The deflection of one of the rollers caused by a change in thickness can then be determined by a sensing element. This method may be useful for fiber bands with a constant width. It is not suitable for relatively thin yarns since changes in thickness in the axial direction can only be detected if the rollers are constructed as key and slot rollers as in the prior art.
It is also known to perform measurements of the mass with an arrangement consisting of light transmitter and light receiver (DE 29 12 558 C2). However, this can only be used for measuring optical characteristics due to surface reflections which then do not reproduce the mass or mass per length of material. Falsifications can occur, e.g. in the case of fluctuations of the color of the rope to be measured. This method according to the prior art is also primarily intended for fiber bands.
This defect is also present in a method in which sound is transmitted through the material and changes in the properties of the material are inferred from the change in attenuation (DE 32 37 357 C2). An unambiguous determination of the mass is not possible by this means since the attenuation can also be influenced by other properties, e.g. the moisture of the material. In addition, this method cannot really be used for relatively thin yarns since it is not possible to direct the total sound through the yarn.
Furthermore, it is known to allow the rope-like material to pass through two plates of a capacitor (DE-OS 20 41 044). Such capacitive measuring methods have the disadvantage that the signals respond very sensitively to changes in the moisture because of the high dielectric constant of water. As a result, it is not possible to compensate for the influence of moisture variations. Before the capacitive measurement, therefore, the material must be stabilized to a precisely defined and known moisture value which can easily require one to two days even with uniform temperatures and other constant conditions. It is therefore not possible to determine quality quickly. The moisture fluctuations are all the more disturbing the closer to production the textile material is examined in the test station, that is to say if it is not possible to ensure that the material is sufficiently homogenized. An accurate image of the quality of the current product which is free of moisture fluctuations is only obtained after it has been stored for a sufficiently long period of time under corresponding conditions. Even then, however, moisture inhomogeneities set a clear limit to the precision of measurements due to variable pore structures which occur in all products.
In a rope material testing method of the type employing a microwave field (WO 00/12974), the density of the fibrous rope material is determined, i.e. the mass per unit volume is measured. If the volume of the material which is being measured in each case changes, this density determination is only possible if the volume of the sample in the measuring field is known in each case. In addition, the location of the measured volume of the material must be kept exactly constant by mechanical sample guidance, since falsified signals are obtained if the rope material migrates into areas of lesser microwave intensities. If the cross-sectional volume of the sample changes, this must either be detected by a parallel volume measurement or taken into consideration by recalibration for the density measurement. In many cases, the density is also of subordinate significance if the material will later be compressed in any case, that is to say brought to a greater density. The density is, therefore, less suitable for testing quality.